This application is based on application No. 10-245119 filed in Japan on Aug. 31, 1998, the content of which incorporated hereinto by reference.
This invention relates to a battery in which a lead (an electrically conducting lead, not the element Pb) plate connected to an electrode assembly is welded to the bottom plate of an external case by an energy beam such as a laser.
The following describes fabrication of a prior art battery in which a lead plate connected to an electrode assembly is welded to the bottom plate of an external case.
(1) A laminate of positive electrode plate, negative electrode plate, and separator in between, is rolled into a spiral shape to form the electrode assembly. The spiral shaped electrode assembly is formed with a center hole to insert an electrode rod for weld connection.
(2) The electrode assembly is inserted into a circular cylindrical external case with a bottom.
(3) A lead plate connected to the bottom of the electrode assembly is weld attached to connect it to the bottom of the external case. As shown in FIG. 1, an electrode rod 2 for weld connection is inserted into the electrode assembly 1 center hole, and the lead plate 4 is pushed by the electrode rod 2 against the bottom plate of the external case 5 and welded.
(4) A lead plate which draws out of the top of the electrode assembly 1 is connected to an electrode on a sealing lid which closes off the opening at the top of the external case 5. After the external case is filled with electrolyte, the sealing lid is fixed to the opening in the external case. The external case is sealed in an airtight fashion by the sealing lid.
This process has the characteristic that the lead plate 4 connected to the electrode assembly 1 can be reliably welded and fixed to the bottom plate of the external case 5. However, a battery of this configuration must be provided with a center hole in the middle of the electrode assembly 1, and this center hole must have a diameter larger than the electrode rod for weld connection. Therefore, the actual volume of the electrode assembly is reduced and the battery""s capacity is decreased. Increasing battery capacity by reducing the size of the electrode assembly center hole may be considered, but when center hole size is reduced, fitting the electrode rod in the center hole becomes a problem.
Technology for connecting a lead plate to the bottom of an external case by laser welding from outside the case has been developed to eliminate the drawbacks of a battery with the configuration described above (Japanese Non-examined Patent Publications No. 4-162351 issued on Jun. 5, 1992 and No. 8-293299 issued on Nov. 5, 1996). These and other disclosures cite batteries which do not use an electrode rod for weld connection. As shown in FIG. 2, an energy beam such as a laser is applied to the bottom plate 25A of the external case 25 from outside the case. The energy beam fuses a portion of the bottom plate 25A and the lead plate 24 to weld and attach the lead plate 24 to the bottom plate 25A.
As shown in FIG. 2, there is no need to provide a center hole in the electrode assembly 21 of a battery in which an energy beam, such as a laser beam, is applied from outside the case to weld the lead plate to the bottom plate. Consequently, this type of battery has the characteristic that the actual electrode assembly volume and battery discharge capacity can be increased. However, in this type of battery in which the lead plate is welded from outside the external case, the lead plate can fail to reliably weld to the bottom plate. For example, with the electrode assembly inserted into the external case, if the lead plate is separated from the bottom plate, the bottom plate of the external case will fuse but the lead pipe will not, and the energy beam will not be able to reliably weld the lead plate to the bottom plate. In addition, if foreign material or contamination is between the lead plate and bottom plate, the energy beam will also fail to make a reliable weld. In particular, whether or not the lead plate is welded to the bottom plate and what kind of attachment is made, cannot be determined from outside this type of battery. Since evaluation of battery quality is difficult, it is extremely important to make weld attachments more reliably.
This invention was developed to solve these types of problems. It is thus a primary object of the present invention to provide a battery that can reliably weld a lead plate do an external case.
The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings.
The battery has an electrode assembly inserted into a cylindrical external case. A lead plate connected to the electrode assembly is welded to the inner surface of the external case by an energy beam applied from outside the external case.
Further, the battery of the present invention is provided with a projection which projects from the inner surface of the external case. An energy beam is applied to the projection from outside the external case to weld attach the inner surface of the projection to the lead plate.
A battery of this configuration has the characteristic that the lead plate can be reliably welded to the external case. This is because the projection in the external case makes reliable contact with the lead plate. The external case and lead plate can be reliably welded by application of an energy beam, such as a laser, to the projection which has its inner surface in contact with the lead plate. In particular, a battery, in which the lead plate and external case can be reliably contacted and welded, also reliably prevents separation of the lead plate and external case due to mechanical shock.
In the battery of the present invention, the projection is disposed in a still more preferable arrangement for contact and weld to the lead plate by curving the projecting surface to its center or by making a conical shaped projection.
Further, the lead plate of the battery can be provided with a flexible deforming piece, and the projection in the external case can be welded to this flexible deforming piece. In addition, the flexible deforming piece can jut outwards towards the projection in the external case to further improve connection of the lead plate and the external case.
Anti-corrosive coating can be used to coat the region of the battery where the energy beam is applied from outside the external case. This effectively prevents corrosion of the region of energy beam application, and contact resistance problems can be avoided via the anti-corrosive coating.